Control systems are known in which a load is driven by a set of field-effect transducers of the insulated-gate type (IGFET) which are connected in a so-called bootstrap circuit. Thus, a capacitor is inserted between the gate and a main electrode (source) of an IGFET to feed back changes in the output voltage to its input; this requires, of course, that the input inpedance of the load connected to the source be high enough to cause a significant instantaneous change of the IGFET output voltage in response to a corresponding input signal. As a result, the output voltage applied to the load follows closely the input signal (or combination of input signals) delivered to the driving IGFET so that a system of this character is incapable of performing a switching function changing the load voltage for a prolonged period in response to a short trigger pulse.